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Beginning today, there will be a small change in how sessions are calculated in Google Analytics. We think this update will lead to a clearer understanding of website interactions. We also want to explain how these changes might impact your reports.

What’s changing?

Currently, Google Analytics ends a session when:

More than 30 minutes have elapsed between pageviews for a single visitor.

At the end of a day.

When a visitor closes their browser.

If any of these events occur, then the next pageview from the visitor will start a new session.

In the new model, Google Analytics will end a session when:

More than 30 minutes have elapsed between pageviews for a single visitor.

As before, if any of these events occur, then the next pageview from the user will be the start of a new session.

How will this affect my Google Analytics data?

This change only applies for visits going forward from today, and your historical data will not change. We’re bringing the definition of session in line with the common definition of a visit. If a visitor leaves your site and returns soon after with a different traffic source value, each visit will be measured with its own session.

Since Google Analytics will start new sessions for all new campaign information, sessions will now have the more accurate attribution information. This will be especially helpful if you use Multi-Channel Funnels. Additionally, by continuing a session when the user closes their browser for only a very short time, sessions will more accurately model a user’s engagement with the website. Overall, this change may slightly increase the number of visits. Based on our research, most users will see less than a 1% change.

We are excited about this update, and look forward to providing you with a better understanding of your website activity. Please leave any question about the change in the comments.

Update 8/17/2011 2:10 PM PST:

We identified an issue responsible for unexpected traffic changes following our recent update to how sessions are defined in Google Analytics. A fix was released at 2pm PST Tuesday August 16th.

The issue affected some sites using the following configurations:

1. If a user comes to a customer’s site with a space in some part of their traffic source data, then revisit the same landing page during that session by refreshing the page or later pressing the back button, a new session will be created for every hit to that page. (Clicking a link elsewhere on the site that leads back to the page should not matter.)

2. Google Analytics implementations using multiple trackers (an unsupported configuration) are also affected when a space is included in the traffic source data. These sites will see fewer visits from new visitors, and more visits from returning visitors (with some variation due to different implementations).

Again, a fix for this issue was released yesterday. Please let us know if you continue to see unexpected traffic changes. We apologize for the inconvenience and thank you for your patience and continued support.